Energy efficient processor core architecture for image processor

ABSTRACT

An apparatus that includes a program controller to fetch and issue instructions is described. The apparatus includes an execution lane having at least one execution unit to execute the instructions. The execution lane is part of an execution lane array that is coupled to a two dimensional shift register array structure, wherein, execution lane s of the execution lane array are located at respective array locations and are coupled to dedicated registers at same respective array locations in the two-dimensional shift register array.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/595,632, filed May 15, 2017, which is a continuation of U.S. patentapplication Ser. No. 14/694,815, filed on Apr. 23, 2015, the entirecontents of which are hereby incorporated by reference.

FIELD OF INVENTION

The field of invention pertains generally to image processing, and, morespecifically, to an energy efficient processor core architecture for animage processor.

BACKGROUND

Image processing typically involves the processing of pixel values thatare organized into an array. Here, a spatially organized two dimensionalarray captures the two dimensional nature of images (additionaldimensions may include time (e.g., a sequence of two dimensional images)and data type (e.g., colors). In a typical scenario, the arrayed pixelvalues are provided by a camera that has generated a still image or asequence of frames to capture images of motion. Traditional imageprocessors typically fall on either side of two extremes.

A first extreme performs image processing tasks as software programsexecuting on a general purpose processor or general purpose-likeprocessor (e.g., a general purpose processor with vector instructionenhancements). Although the first extreme typically provides a highlyversatile application software development platform, its use of finergrained data structures combined with the associated overhead (e.g.,instruction fetch and decode, handling of on-chip and off-chip data,speculative execution) ultimately results in larger amounts of energybeing consumed per unit of data during execution of the program code.

A second, opposite extreme applies fixed function hardwired circuitry tomuch larger blocks of data. The use of larger (as opposed to finergrained) blocks of data applied directly to custom designed circuitsgreatly reduces power consumption per unit of data. However, the use ofcustom designed fixed function circuitry generally results in a limitedset of tasks that the processor is able to perform. As such, the widelyversatile programming environment (that is associated with the firstextreme) is lacking in the second extreme.

A technology platform that provides for both highly versatileapplication software development opportunities combined with improvedpower efficiency per unit of data remains a desirable yet missingsolution.

SUMMARY

An apparatus is described. The apparatus includes a program controllerto fetch and issue instructions. The apparatus includes an executionlane having at least one execution unit to execute the instructions. Theexecution lane is part of an execution lane array that is coupled to atwo dimensional shift register array structure, wherein, execution lanes of the execution lane array are located at respective array locationsand are coupled to dedicated registers at same respective arraylocations in the two-dimensional shift register array.

LIST OF FIGURES

The following description and accompanying drawings are used toillustrate embodiments of the invention. In the drawings:

FIG. 1 shows an embodiment of an image processor hardware architecture;

FIGS. 2a, 2b, 2c, 2d and 2e depict the parsing of image data into a linegroup, the parsing of a line group into a sheet and the operationperformed on a sheet with overlapping stencils;

FIG. 3a shows an embodiment of a stencil processor;

FIG. 3b shows an embodiment of a instruction word of the stencilprocessor;

FIG. 4 shows an embodiment of a data computation unit within a stencilprocessor;

FIGS. 5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h, 5i, 5j and 5k depict an example ofthe use of a two-dimensional shift array and an execution lane array todetermine a pair of neighboring output pixel values with overlappingstencils;

FIG. 6a shows an embodiment of a unit cell for an integrated executionlane array and two-dimensional shift array;

FIG. 6b shows an embodiment of an execution lane ALU;

FIG. 7a depicts a first two dimensional register array structureinterconnection scheme;

FIG. 7b depicts a second two dimensional register array structureinterconnection scheme;

FIG. 8a depicts a first row or column of a two-dimensional registerarray structure;

FIG. 8b depicts a second row or column of a two-dimensional registerarray structure;

FIG. 8c depicts the row of FIG. 8b coupled to a memory unit;

FIG. 8d shows another toroid embodiment;

FIG. 8e shows a power conservation circuit;

FIG. 9 pertains to operation at higher bit widths that the registerswithin the register file;

FIG. 10 pertains to controlling memory operations within the executionlane array;

FIG. 11 shows an embodiment of a computing system.

DETAILED DESCRIPTION a. Image Processor Hardware Architecture andOperation

FIG. 1 shows an embodiment of an architecture 100 for an image processorimplemented in hardware. The image processor may be targeted, forexample, by a compiler that converts program code written for a virtualprocessor within a simulated environment into program code that isactually executed by the hardware processor. As observed in FIG. 1, thearchitecture 100 includes a plurality of line buffer units 101_1 through101_M interconnected to a plurality of stencil processor units 102_1through 102_N and corresponding sheet generator units 103_1 through103_N through a network 104 (e.g., a network on chip (NOC) including anon chip switch network, an on chip ring network or other kind ofnetwork). In an embodiment, any line buffer unit may connect to anysheet generator and corresponding stencil processor through the network104.

In an embodiment, program code is compiled and loaded onto acorresponding stencil processor 102 to perform the image processingoperations earlier defined by a software developer (program code mayalso be loaded onto the stencil processor's associated sheet generator103, e.g., depending on design and implementation). In at least someinstances an image processing pipeline may be realized by loading afirst kernel program for a first pipeline stage into a first stencilprocessor 102_1, loading a second kernel program for a second pipelinestage into a second stencil processor 102_2, etc. where the first kernelperforms the functions of the first stage of the pipeline, the secondkernel performs the functions of the second stage of the pipeline, etc.and additional control flow methods are installed to pass output imagedata from one stage of the pipeline to the next stage of the pipeline.

In other configurations, the image processor may be realized as aparallel machine having two or more stencil processors 102_1, 102_2operating the same kernel program code. For example, a highly dense andhigh data rate stream of image data may be processed by spreading framesacross multiple stencil processors each of which perform the samefunction.

In yet other configurations, essentially any DAG of kernels may beloaded onto the hardware processor by configuring respective stencilprocessors with their own respective kernel of program code andconfiguring appropriate control flow hooks into the hardware to directoutput images from one kernel to the input of a next kernel in the DAGdesign.

As a general flow, frames of image data are received by a macro I/O unit105 and passed to one or more of the line buffer units 101 on a frame byframe basis. A particular line buffer unit parses its frame of imagedata into a smaller region of image data, referred to as a “a linegroup”, and then passes the line group through the network 104 to aparticular sheet generator. A complete or “full” singular line group maybe composed, for example, with the data of multiple contiguous completerows or columns of a frame (for simplicity the present specificationwill mainly refer to contiguous rows). The sheet generator furtherparses the line group of image data into a smaller region of image data,referred to as a “sheet”, and presents the sheet to its correspondingstencil processor.

In the case of an image processing pipeline or a DAG flow having asingle input, generally, input frames are directed to the same linebuffer unit 101_1 which parses the image data into line groups anddirects the line groups to the sheet generator 103_1 whose correspondingstencil processor 102_1 is executing the code of the first kernel in thepipeline/DAG. Upon completion of operations by the stencil processor102_1 on the line groups it processes, the sheet generator 103_1 sendsoutput line groups to a “downstream” line buffer unit 101_2 (in some usecases the output line group may be sent back to the same line bufferunit 101_1 that earlier had sent the input line groups).

One or more “consumer” kernels that represent the next stage/operationin the pipeline/DAG executing on their own respective other sheetgenerator and stencil processor (e.g., sheet generator 103_2 and stencilprocessor 102_2) then receive from the downstream line buffer unit 101_2the image data generated by the first stencil processor 102_1. In thismanner, a “producer” kernel operating on a first stencil processor hasits output data forwarded to a “consumer” kernel operating on a secondstencil processor where the consumer kernel performs the next set oftasks after the producer kernel consistent with the design of theoverall pipeline or DAG.

A stencil processor 102 is designed to simultaneously operate onmultiple overlapping stencils of image data. The multiple overlappingstencils and internal hardware processing capacity of the stencilprocessor effectively determines the size of a sheet. Here, within astencil processor 102, arrays of execution lanes operate in unison tosimultaneously process the image data surface area covered by themultiple overlapping stencils.

As will be described in more detail below, in various embodiments,sheets of image data are loaded into a two-dimensional register arraystructure within the stencil processor 102. The use of sheets and thetwo-dimensional register array structure is believed to effectivelyprovide for power consumption improvements by moving a large amount ofdata into a large amount of register space as, e.g., a single loadoperation with processing tasks performed directly on the dataimmediately thereafter by an execution lane array. Additionally, the useof an execution lane array and corresponding register array provide fordifferent stencil sizes that are easily programmable/configurable.

FIGS. 2a through 2e illustrate at a high level embodiments of both theparsing activity of a line buffer unit 101, the finer grained parsingactivity of a sheet generator unit 103 as well as the stencil processingactivity of the stencil processor 102 that is coupled to the sheetgenerator unit 103.

FIG. 2a depicts an embodiment of an input frame of image data 201. FIG.2a also depicts an outline of three overlapping stencils 202 (eachhaving a dimension of 3 pixels×3 pixels) that a stencil processor isdesigned to operate over. The output pixel that each stencilrespectively generates output image data for is highlighted in solidblack. For simplicity, the three overlapping stencils 202 are depictedas overlapping only in the vertical direction. It is pertinent torecognize that in actuality a stencil processor may be designed to haveoverlapping stencils in both the vertical and horizontal directions.

Because of the vertical overlapping stencils 202 within the stencilprocessor, as observed in FIG. 2a , there exists a wide band of imagedata within the frame that a single stencil processor can operate over.As will be discussed in more detail below, in an embodiment, the stencilprocessors process data within their overlapping stencils in a left toright fashion across the image data (and then repeat for the next set oflines, in top to bottom order). Thus, as the stencil processors continueforward with their operation, the number of solid black output pixelblocks will grow right-wise horizontally. As discussed above, a linebuffer unit 101 is responsible for parsing a line group of input imagedata from an incoming frame that is sufficient for the stencilprocessors to operate over for an extended number of upcoming cycles. Anexemplary depiction of a line group is illustrated as a shaded region203. In an embodiment, the line buffer unit 101 can comprehend differentdynamics for sending/receiving a line group to/from a sheet generator.For example, according to one mode, referred to as “full group”, thecomplete full width lines of image data are passed between a line bufferunit and a sheet generator. According to a second mode, referred to as“virtually tall”, a line group is passed initially with a subset of fullwidth rows. The remaining rows are then passed sequentially in smaller(less than full width) pieces.

With the line group 203 of the input image data having been defined bythe line buffer unit and passed to the sheet generator unit, the sheetgenerator unit further parses the line group into finer sheets that aremore precisely fitted to the hardware limitations of the stencilprocessor. More specifically, as will be described in more detailfurther below, in an embodiment, each stencil processor consists of atwo dimensional shift register array. The two dimensional shift registerarray essentially shifts image data “beneath” an array of executionlanes where the pattern of the shifting causes each execution lane tooperate on data within its own respective stencil (that is, eachexecution lane processes on its own stencil of information to generatean output for that stencil). In an embodiment, sheets are surface areasof input image data that “fill” or are otherwise loaded into the twodimensional shift register array.

As will be described in more detail below, in various embodiments, thereare actually multiple layers of two dimensional register data that canbe shifted on any cycle. For convenience, much of the presentdescription will simply use the term “two-dimensional shift register”and the like to refer to structures that have one or more such layers oftwo-dimensional register data that can be shifted.

Thus, as observed in FIG. 2b , the sheet generator parses an initialsheet 204 from the line group 203 and provides it to the stencilprocessor (here, the sheet of data corresponds to the shaded region thatis generally identified by reference number 204). As observed in FIGS.2c and 2d , the stencil processor operates on the sheet of input imagedata by effectively moving the overlapping stencils 202 in a left toright fashion over the sheet. As of FIG. 2d , the number of pixels forwhich an output value could be calculated from the data within the sheetis exhausted (no other pixel positions can have an output valuedetermined from the information within the sheet). For simplicity theborder regions of the image have been ignored.

As observed in FIG. 2e the sheet generator then provides a next sheet205 for the stencil processor to continue operations on. Note that theinitial positions of the stencils as they begin operation on the nextsheet is the next progression to the right from the point of exhaustionon the first sheet (as depicted previously in FIG. 2d ). With the newsheet 205, the stencils will simply continue moving to the right as thestencil processor operates on the new sheet in the same manner as withthe processing of the first sheet.

Note that there is some overlap between the data of the first sheet 204and the data of the second sheet 205 owing to the border regions ofstencils that surround an output pixel location. The overlap could behandled simply by the sheet generator re-transmitting the overlappingdata twice. In alternate implementations, to feed a next sheet to thestencil processor, the sheet generator may proceed to only send new datato the stencil processor and the stencil processor reuses theoverlapping data from the previous sheet.

b. Stencil Processor Design and Operation

FIG. 3a shows an embodiment of a stencil processor architecture 300. Asobserved in FIG. 3a , the stencil processor includes a data computationunit 301, a scalar processor 302 and associated memory 303 and an I/Ounit 304. The data computation unit 301 includes an array of executionlanes 305, a two-dimensional shift array structure 306 and separaterandom access memories 307 associated with specific rows or columns ofthe array.

The I/O unit 304 is responsible for loading “input” sheets of datareceived from the sheet generator into the data computation unit 301 andstoring “output” sheets of data from the stencil processor into thesheet generator. In an embodiment the loading of sheet data into thedata computation unit 301 entails parsing a received sheet intorows/columns of image data and loading the rows/columns of image datainto the two dimensional shift register structure 306 or respectiverandom access memories 307 of the rows/columns of the execution lanearray (described in more detail below). If the sheet is initially loadedinto memories 307, the individual execution lanes within the executionlane array 305 may then load sheet data into the two-dimensional shiftregister structure 306 from the random access memories 307 whenappropriate (e.g., as a load instruction just prior to operation on thesheet's data). Upon completion of the loading of a sheet of data intothe register structure 306 (whether directly from a sheet generator orfrom memories 307), the execution lanes of the execution lane array 305operate on the data and eventually “write back” finished data as a sheetdirectly back to the sheet generator, or, into the random accessmemories 307. If the later the I/O unit 304 fetches the data from therandom access memories 307 to form an output sheet which is thenforwarded to the sheet generator.

The scalar processor 302 includes a program controller 309 that readsthe instructions of the stencil processor's program code from scalarmemory 303 and issues the instructions to the execution lanes in theexecution lane array 305. In an embodiment, a single same instruction isbroadcast to all execution lanes within the array 305 to effect aSIMD-like behavior from the data computation unit 301. In an embodiment,the instruction format of the instructions read from scalar memory 303and issued to the execution lanes of the execution lane array 305includes a very-long-instruction-word (VLIW) type format that includesmore than one opcode per instruction. In a further embodiment, the VLIWformat includes both an ALU opcode that directs a mathematical functionperformed by each execution lane's ALU (which, as described below, in anembodiment may specify more than one traditional ALU operation) and amemory opcode (that directs a memory operation for a specific executionlane or set of execution lanes).

The term “execution lane” refers to a set of one or more execution unitscapable of executing an instruction (e.g., logic circuitry that canexecute an instruction). An execution lane can, in various embodiments,include more processor-like functionality beyond just execution units,however. For example, besides one or more execution units, an executionlane may also include logic circuitry that decodes a receivedinstruction, or, in the case of more MIMD-like designs, logic circuitrythat fetches and decodes an instruction. With respect to MIMD-likeapproaches, although a centralized program control approach has largelybeen described herein, a more distributed approach may be implemented invarious alternative embodiments (e.g., including program code and aprogram controller within each execution lane of the array 305).

The combination of an execution lane array 305, program controller 309and two dimensional shift register structure 306 provides a widelyadaptable/configurable hardware platform for a broad range ofprogrammable functions. For example, application software developers areable to program kernels having a wide range of different functionalcapability as well as dimension (e.g., stencil size) given that theindividual execution lanes are able to perform a wide variety offunctions and are able to readily access input image data proximate toany output array location.

Apart from acting as a data store for image data being operated on bythe execution lane array 305, the random access memories 307 may alsokeep one or more look-up tables. In various embodiments one or morescalar look-up tables may also be instantiated within the scalar memory303.

A scalar look-up involves passing the same data value from the samelook-up table from the same index to each of the execution lanes withinthe execution lane array 305. In various embodiments, the VLIWinstruction format described above is expanded to also include a scalaropcode that directs a look-up operation performed by the scalarprocessor into a scalar look-up table. The index that is specified foruse with the opcode may be an immediate operand or fetched from someother data storage location. Regardless, in an embodiment, a look-upfrom a scalar look-up table within scalar memory essentially involvesbroadcasting the same data value to all execution lanes within theexecution lane array 305 during the same clock cycle. Additional detailsconcerning use and operation of look-up tables is provided furtherbelow.

FIG. 3b summarizes the VLIW instruction word embodiments(s) discussedabove. As observed in FIG. 3b , the VLIW instruction word formatincludes fields for three separate instructions: 1) a scalar instruction351 that is executed by the scalar processor; 2) an ALU instruction 352that is broadcasted and executed in SIMD fashion by the respective ALUswithin the execution lane array; and, 3) a memory instruction 353 thatis broadcasted and executed in a partial SIMD fashion (e.g., ifexecution lanes along a same row in the execution lane array share asame random access memory, then one execution lane from each of thedifferent rows actually execute the instruction (the format of thememory instruction 353 may include an operand that identifies whichexecution lane from each row executes the instruction)

A field 354 for one or more immediate operands is also included. Whichof the instructions 351, 352, 353 use which immediate operandinformation may be identified in the instruction format. Each ofinstructions 351, 352, 353 also include their own respective inputoperand and resultant information (e.g., local registers for ALUoperations and a local register and a memory address for memory accessinstructions). In an embodiment, the scalar instruction 351 is executedby the scalar processor before the execution lanes within the executionlane array execute either of the other to instructions 352, 353. Thatis, the execution of the VLIW word includes a first cycle upon which thescalar instruction 351 is executed followed by a second cycle upon withthe other instructions 352, 353 may be executed (note that in variousembodiments instructions 352 and 353 may be executed in parallel).

In an embodiment, the scalar instructions executed by the scalarprocessor include commands issued to the sheet generator to load/storesheets from/into the memories or 2D shift register of the datacomputation unit. Here, the sheet generator's operation can be dependenton the operation of the line buffer unit or other variables that preventpre-runtime comprehension of the number of cycles it will take the sheetgenerator to complete any command issued by the scalar processor. Assuch, in an embodiment, any VLIW word whose scalar instruction 351corresponds to or otherwise causes a command to be issued to the sheetgenerator also includes no-operation (NOOP) instructions in the othertwo instruction field 352, 353. The program code then enters a loop ofNOOP instructions for instruction fields 352, 353 until the sheetgenerator completes its load/store to/from the data computation unit.Here, upon issuing a command to the sheet generator, the scalarprocessor may set a bit of an interlock register that the sheetgenerator resets upon completion of the command. During the NOOP loopthe scalar processor monitors the bit of the interlock bit. When thescalar processor detects that the sheet generator has completed itscommand normal execution begins again.

FIG. 4 shows an embodiment of a data computation component 401. Asobserved in FIG. 4, the data computation component 401 includes an arrayof execution lanes 405 that are logically positioned “above” atwo-dimensional shift register array structure 406. As discussed above,in various embodiments, a sheet of image data provided by a sheetgenerator is loaded into the two-dimensional shift register 406. Theexecution lanes then operate on the sheet data from the registerstructure 406.

The execution lane array 405 and shift register structure 406 are fixedin position relative to one another. However, the data within the shiftregister array 406 shifts in a strategic and coordinated fashion tocause each execution lane in the execution lane array to process adifferent stencil within the data. As such, each execution lanedetermines the output image value for a different pixel in the outputsheet being generated. From the architecture of FIG. 4 it should beclear that overlapping stencils are not only arranged vertically butalso horizontally as the execution lane array 405 includes verticallyadjacent execution lanes as well as horizontally adjacent executionlanes.

Some notable architectural features of the data computation unit 401include the shift register structure 406 having wider dimensions thanthe execution lane array 405. That is, there is a “halo” of registers409 outside the execution lane array 405. Although the halo 409 is shownto exist on two sides of the execution lane array, depending onimplementation, the halo may exist on less (one) or more (three or four)sides of the execution lane array 405. The halo 405 serves to provide“spill-over” space for data that spills outside the bounds of theexecution lane array 405 as the data is shifting “beneath” the executionlanes 405. As a simple case, a 5×5 stencil centered on the right edge ofthe execution lane array 405 will need four halo register locationsfurther to the right when the stencil's leftmost pixels are processed.For ease of drawing, FIG. 4 shows the registers of the right side of thehalo as only having horizontal shift connections and registers of thebottom side of the halo as only having vertical shift connections when,in a nominal embodiment, registers on either side (right, bottom) wouldhave both horizontal and vertical connections.

Additional spill-over room is provided by random access memories 407that are coupled to each row and/or each column in the array, orportions thereof (E.g., a random access memory may be assigned to a“region” of the execution lane array that spans 4 execution lanes rowwise and 2 execution lanes column wise. For simplicity the remainder ofthe application will refer mainly to row and/or column based allocationschemes). Here, if an execution lane's kernel operations require it toprocess pixel values outside of the two-dimensional shift register array406 (which some image processing routines may require) the plane ofimage data is able to further spill-over, e.g., from the halo region 409into random access memory 407. For example, consider a 6×6 stencil wherethe hardware includes a halo region of only four storage elements to theright of an execution lane on the right edge of the execution lanearray. In this case, the data would need to be shifted further to theright off the right edge of the halo 409 to fully process the stencil.Data that is shifted outside the halo region 409 would then spill-overto random access memory 407. Other applications of the random accessmemories 407 and the stencil processor of FIG. 3 are provided furtherbelow.

FIGS. 5a through 5k demonstrate a working example of the manner in whichimage data is shifted within the two dimensional shift register array“beneath” the execution lane array as alluded to above. As observed inFIG. 5a , the data contents of the two dimensional shift array aredepicted in a first array 507 and the execution lane array is depictedby a frame 505. Also, two neighboring execution lanes 510 within theexecution lane array are simplistically depicted. In this simplisticdepiction 510, each execution lane includes a register R1 that canaccept data from the shift register, accept data from an ALU output(e.g., to behave as an accumulator across cycles), or write output datainto an output destination.

Each execution lane also has available, in a local register R2, thecontents “beneath” it in the two dimensional shift array. Thus, R1 is aphysical register of the execution lane while R2 is a physical registerof the two dimensional shift register array. The execution lane includesan ALU that can operate on operands provided by R1 and/or R2. As will bedescribed in more detail further below, in an embodiment the shiftregister is actually implemented with multiple (a “depth” of)storage/register elements per array location but the shifting activityis limited to one plane of storage elements (e.g., only one plane ofstorage elements can shift per cycle). FIGS. 5a through 5k depict one ofthese deeper register locations as being used to store the resultant Xfrom the respective execution lanes. For illustrative ease the deeperresultant register is drawn alongside rather than beneath itscounterpart register R2.

FIGS. 5a through 5k focus on the calculation of two stencils whosecentral position is aligned with the pair of execution lane positions511 depicted within the execution lane array. For ease of illustration,the pair of execution lanes 510 are drawn as horizontal neighbors whenin fact, according to the following example, they are verticalneighbors.

As observed initially in FIG. 5a , the execution lanes are centered ontheir central stencil locations. FIG. 5b shows the object code executedby both execution lanes. As observed in FIG. 5b the program code of bothexecution lanes causes the data within the shift register array to shiftdown one position and shift right one position. This aligns bothexecution lanes to the upper left hand corner of their respectivestencils. The program code then causes the data that is located (in R2)in their respective locations to be loaded into R1.

As observed in FIG. 5c the program code next causes the pair ofexecution lanes to shift the data within the shift register array oneunit to the left which causes the value to the right of each executionlane's respective position to be shifted into each execution lane'position. The value in R1 (previous value) is then added with the newvalue that has shifted into the execution lane's position (in R2). Theresultant is written into R1. As observed in FIG. 5d the same process asdescribed above for FIG. 5c is repeated which causes the resultant R1 tonow include the value A+B+C in the upper execution lane and F+G+H in thelower execution lane. At this point both execution lanes have processedthe upper row of their respective stencils. Note the spill-over into ahalo region on the left side of the execution lane array (if one existson the left hand side) or into random access memory if a halo regiondoes not exist on the left hand side of the execution lane array.

As observed in FIG. 5e , the program code next causes the data withinthe shift register array to shift one unit up which causes bothexecution lanes to be aligned with the right edge of the middle row oftheir respective stencils. Register R1 of both execution lanes currentlyincludes the summation of the stencil's top row and the middle row'srightmost value. FIGS. 5f and 5g demonstrate continued progress movingleftwise across the middle row of both execution lane's stencils. Theaccumulative addition continues such that at the end of processing ofFIG. 5g both execution lanes include the summation of the values of thetop row and the middle row of their respective stencils.

FIG. 5h shows another shift to align each execution lane with itscorresponding stencil's lowest row. FIGS. 5i and 5j show continuedshifting to complete processing over the course of both execution lanes'stencils. FIG. 5k shows additional shifting to align each execution lanewith its correct position in the data array and write the resultantthereto.

In the example of FIGS. 5a-5k note that the object code for the shiftoperations may include an instruction format that identifies thedirection and magnitude of the shift expressed in (X, Y) coordinates.For example, the object code for a shift up by one location may beexpressed in object code as SHIFT 0, +1. As another example, a shift tothe right by one location may expressed in object code as SHIFT +1, 0.In various embodiments shifts of larger magnitude may also be specifiedin object code (e.g., SHIFT 0, +2). Here, if the 2D shift registerhardware only supports shifts by one location per cycle, the instructionmay be interpreted by the machine to require multiple cycle execution,or, the 2D shift register hardware may be designed to support shifts bymore than one location per cycle. Embodiments of the later are describedin more detail further below.

FIG. 6a shows another, more detailed depiction of the unit cell for thearray execution lane and shift register structure (registers in the haloregion do not include a corresponding execution lane). The executionlane and the register space associated with each location in theexecution lane array is, in an embodiment, implemented by instantiatingthe circuitry observed in FIG. 6a at each node of the execution lanearray. As observed in FIG. 6a , the unit cell includes an execution lane601 coupled to a register file 602 consisting of four registers R2through R5. During any cycle, the execution lane 601 may read from orwrite to any of registers R1 through R5. For instructions requiring twoinput operands the execution lane may retrieve both of operands from anyof R1 through R5.

In an embodiment, the two dimensional shift register structure isimplemented by permitting, during a single cycle, the contents of any of(only) one of registers R2 through R4 to be shifted “out” to one of itsneighbor's register files through output multiplexer 603, and, havingthe contents of any of (only) one of registers R2 through R4 replacedwith content that is shifted “in” from a corresponding one if itsneighbors through input multiplexers 604 such that shifts betweenneighbors are in a same direction (e.g., all execution lanes shift left,all execution lanes shift right, etc.). Although it may be common for asame register to have its contents shifted out and replaced with contentthat is shifted in on a same cycle, the multiplexer arrangement 603, 604permits for different shift source and shift target registers within asame register file during a same cycle.

As depicted in FIG. 6a note that during a shift sequence an executionlane will shift content out from its register file 602 to each of itsleft, right, top and bottom neighbors. In conjunction with the sameshift sequence, the execution lane will also shift content into itsregister file from a particular one of its left, right, top and bottomneighbors. Again, the shift out target and shift in source should beconsistent with a same shift direction for all execution lanes (e.g., ifthe shift out is to the right neighbor, the shift in should be from theleft neighbor).

Although in one embodiment the content of only one register is permittedto be shifted per execution lane per cycle, other embodiments may permitthe content of more than one register to be shifted in/out. For example,the content of two registers may be shifted out/in during a same cycleif a second instance of the multiplexer circuitry 603, 604 observed inFIG. 6a is incorporated into the design of FIG. 6a . Of course, inembodiments where the content of only one register is permitted to beshifted per cycle, shifts from multiple registers may take place betweenmathematical operations by consuming more clock cycles for shiftsbetween mathematical operations (e.g., the contents of two registers maybe shifted between math ops by consuming two shift ops between the mathops).

If less than all the content of an execution lane's register files areshifted out during a shift sequence note that the content of the nonshifted out registers of each execution lane remain in place (do notshift). As such, any non shifted content that is not replaced withshifted in content persists local to the execution lane across theshifting cycle. The memory unit (“M”) observed in each execution lane isused to load/store data from/to the random access memory space that isassociated with the execution lane's row and/or column within theexecution lane array. Here, the M unit acts as a standard M unit in thatit is often used to load/store data that cannot be loaded/stored from/tothe execution lane's own register space. In various embodiments, theprimary operation of the M unit is to write data from a local registerinto memory, and, read data from memory and write it into a localregister.

With respect to the ISA opcodes supported by the ALU unit of thehardware execution lane 601, in various embodiments, the mathematicalopcodes supported by the hardware ALU are integrally tied with (e.g.,substantially the same as) the mathematical opcodes supported by avirtual execution lane (e.g., ADD, SUB, MOV, MUL, MAD, ABS, DIV, SHL,SHR, MIN/MAX, SEL, AND, OR, XOR, NOT). As described just above, memoryaccess instructions can be executed by the execution lane 601 tofetch/store data from/to their associated random access memory.Additionally the hardware execution lane 601 supports shift opinstructions (right, left, up, down) to shift data within the twodimensional shift register structure. As described above, programcontrol instructions are largely executed by the scalar processor of thestencil processor.

FIG. 6b shows an embodiment of a processor ALU. As observed in FIG. 6b ,the processor ALU includes a multiply-add unit 611 and first and secondnominal ALUs 612, 613. The multiply-add unit 611 performs the operation(A*B)+C. The first and second nominal ALUs perform nominal math andlogical operations including comparison operations (e.g., add, subtract,and, or, xor, comparison, minimum, maximum, absolute value, shift). TheALU design can be viewed as having two primary datapaths: a first thatincludes the multiply-add unit 611, a second that includes a dual ALU612, 613 chain. The dual ALU chain 612, 613 permits for more complexinstructions having two operations in a single instruction (e.g., twoADDs in a single instruction; and ADD and a divide (DIV) in a singleinstruction; a subtract (SUB) and an absolute value (ABS) in a singleinstruction, etc.). Input operands are receivable from registers.Various embodiments may include the use of immediate operands that areappended to the opcode. The output resultant is written to a register.

c. 2D Shift Register Embodiments

FIG. 7a depicts an embodiment of a “top down” view of the logical (andpotentially physical) design of a two-dimensional register arraystructure. The “top-down” view of FIG. 7a essentially conforms to theunit cell design embodiment of FIG. 6 in which each register file at aparticular array location is coupled to the register file of its left,right, up and down neighboring unit cell location. That is, for example,as seen in FIG. 7a , register file A is coupled to register files B, C,D and E.

FIG. 7b depicts another embodiment of a “top-down” view of the logical(and potentially physical) design of a two-dimensional register arraystructure. As observed in FIG. 7b , unit cells are not only coupled tonearest vertical and horizontal neighbors, but also “second” nearestvertical and horizontal neighbors. For example, as observed in FIG. 7b ,unit cell A is not only coupled to unit cells B, C, D and E but is alsocoupled to unit cells F, G, H and I. For ease of drawing and viewing,only unit cell A is depicted as having the full set of connectionsneeded to have both nearest and second nearest neighbor coupling. Otherthan unit cell A, only every other unit cell shows second nearestneighbor coupling along any particular row or column (e.g., unit cell Bdoes not depict any second nearest neighbor coupling). The reader willunderstand that a preferred embodiment would include the coupling ofunit cell A for, e.g., all the unit cells within the core andsufficiently away from array edges to support second nearest neighborcoupling.

Having second nearest connection provides for faster propagation of theregister values through the register array. For example, if a registervalue needs to be moved to a unit cell four locations away, the arraystructure of FIG. 7b can accomplish the move in two cycles whereas thearray structure of FIG. 7b can accomplish the same move in only fourcycles. Note that the embodiment of FIG. 7b also has nearest neighborconnections. Thus, the processor instruction set for the structure ofFIG. 7b may be more expansive than the processor instruction set for thestructure of FIG. 7a (the former having one-hop and two-hop MOVinstructions whereas the latter only has one-hop MOV instructions).

It is pertinent to point out that the number and combination ofdifferent numbered hop movements and corresponding array structureembodiments may widely vary from embodiment to embodiment depending onthe appropriate trade off balance between the need for rapid registervalue movement and the tolerance for array structure wiring density.Some embodiments may support nearest third or and/or fourth neighborconnections, others may not (in the case of nearest fourth neighborconnections, e.g., unit cell D would be directly coupled to unit cell Jin FIG. 7b ). Some embodiments may have only nearest neighborconnections and nearest third or farther connections, etc. Conceivably,more elaborate embodiments may even support diagonal connections (e.g.,connecting unit cell A with unit cell K and its other three neighboringcorner unit cells in FIG. 7b ). Those of ordinary skill will recognizethat any of the various, expanded connections amongst unit cells isreadily accomplished by expanding the sources of the inputs to the inputmux structure 604 and expanding the fan-out from the output muxstructure 603 of FIG. 6 a.

FIG. 8a shows an exemplary logical arrangement of registers along a rowor column within a two dimensional register array structure (for ease ofdrawing the register array only has dimensions of 8×8, whereas, inactual practice the dimensions may be much larger). Here, neighboringpixels in an array being processed will be located in numericallyneighboring units cells (e.g., a pair of neighboring pixels in the arraywill be placed in unit cells 3 and 4 rather than 3 and 5). The logicaldesign of FIG. 8a also includes a roll capability by coupling the firstlogical unit cell 1 to the last unit cell 8 through connection 801 (thusthe processors of the execution lane may also include a roll opcode).

Problems may arise however, particularly in the case of arrays of largedimension, if the design of FIG. 8a not only represents the logicaldesign but also represents the physical design. If the approach of FIG.8a also represents the physical design, connection 801 corresponds to anextremely long length wire as compared to the length of the other wiresthat connect unit cell pairs other than pair 1 and 8. This particularwire length outlier can impact circuit timing complications (by slowingdown all shift times between all unit cells to be no less than theslowest 1<->8 shift time, or, introducing complications that recognizemore cycles between 1<->8 shifts than shifts between any otherneighboring unit cells).

FIG. 8b shows an embodiment of an improved physical design for a row orcolumn of a register array structure having the logical design of FIG.8a . Here, a physical design corresponds to actual layout of circuitstructures as opposed to just logical connections (as with a logicaldesign). As observed in FIG. 8b , the physical design amortizes theextra length required by the 1<->8 connection amongst the other unitcell by imposing a toroid design in the logic of the layout. Forexample, although unit cell 1 is physically connected to unit cell 2 topreserve the logic design, unit cell 8 physically sits between them. Theresultant is a maximum wire length between unit cells in the structureof FIG. 8b that is much shorter than the length of wire 801 in FIG. 8a .As such the timing complications of the structure of FIG. 8b avoid thetiming complications of the structure of FIG. 8a mentioned above. In anembodiment, a roll of register content between all unit cells cantranspire within a single cycle.

FIG. 8c shows that the data bus structure between the sheet generator ora random access memory 802 (such as any of RAMs 407 of FIG. 4) and a rowor column of the register array include a kind of swizzling structure803 in order to preserve the correct logic connections to an array orrow having a toroid physical layout. FIG. 8d shows another toroidstructure that can implement 4-hop shifts where the maximum distancetraveled by any register value is 4 unit cells. Here, it should be clearthat another swizzling like data bus would exist between the registersof FIG. 8d and the sheet generator or RAM. As such, a feature of theimplementation of a toroid physical layout is the existence of swizzlingby a data bus that connects inputs that are arranged in logical order.

FIG. 8e shows special fan-out circuitry from the output multiplexer 804of a unit cell of the shift array structure. Here, output multiplexer804 can be viewed as akin to output multiplexer 603 of FIG. 6a . As theshift array is designed to support more and more connections (one hop,two hop, etc.), the fan-out of the output multiplexer 804 grows. As thefan-out of the multiplexer 804 grows, power consumption may become moreand more of an issue. FIG. 8e shows an output multiplexer 804 for ashift register array that fully supports both one hop and twoconnections. Here, without the presence of the logic gates observed inFIG. 8e , a new output at multiplexer 804 (e.g., a new shift out value)would be broadcast to eight different locations (left neighbor, rightneighbor, . . . , 2 hop bottom neighbor). Here, as is understood in theart, a change in data across a run length of wire in a logical circuitcorresponds to “switching activity” which, in turn, consumes power.

The presence of the eight logic gates observed at the output ofmultiplexer 804 are designed to prevent any such data change except onthe actual wire that corresponds to the shift direction. For example, ifthe shift direction is one-hop to the right, only the gate that iscoupled to the immediate right neighbor will permit the output of themultiplexer 804 to pass. All other logic gates will prevent the datavalue from propagating to the other nodes (where the shift value is notneeded) and reduce power consumption of the shift operation in theprocess.

d. Additional Execution Lane Operations of Note

FIG. 9 pertains to a technique used to permit the execution lane swithin the execution lane array to handle different data bit widths.Here, as is understood in the art, greater dynamic range is achieved byincreasing the bit width of the data values (a 16 bit value can expressvalues with greater dynamic range than an 8 bit value can). In anembodiment, the stencil processors are expected to operate on imageshaving different bit widths such as 8, 16 or 32 bit pixel values. Assuch, according to one approach, the execution lane s themselves are 32bit machines in the sense that the execution lane s internally canhandle 32 bit operands.

However, to decrease the size and complexity of the two dimensionalshift register, the individual storage elements of the registers withineach execution lane's register file are limited to 8 bits. In the caseof 8 bit image data there is no issue because an entire sheet of datacan fit in one register of the register file. By contrast, in the caseof 16 or 32 bit operands, the sheet generator generates multiple sheetsto appropriately express the input operand data set.

For example, as depicted in FIG. 9 in the case of 16 bit input operandsthe sheet generator will generate a HI half sheet and a LO half sheet.The HI half sheet contains the upper 8 bits of each data item at thecorrect array location. The LO half sheet contains the lower 8 bits ofeach data item at the correct array location. 16 bit operations are thenperformed by loading both sheets into the stencil processor andinforming the execution lane hardware (e.g., via an immediate value inthe program code) that 16 bit operation is to take place. Here, as justone possible mode of operation, both the HI and LO sheets are loaded intwo different registers of each execution lane's register file.

The execution lane units are able to internally construct the correctoperands by first reading from one of the register file locations andappending the data therein with the data read from another of theregister file locations. Similarly, in the write direction, theexecution lane units will have to perform two writes. Specifically, afirst write of the lower 8 bits to a first register of the register filecontaining the LO sheet and then a second write of the upper 8 bits to asecond register of the register file containing the HI sheet.

Recall from previous discussions that in various embodiment shifts fromthe content of only one register is permitted to be shifted per cycle.In these cases, in order to move 16 bit data values around the twodimensional shift register structure, two cycles are consumed per shiftsequence (between math ops) rather than one cycle in the case of 8 bitdata values. That is, in the nominal case of 8 bit data values, all datacan be shifted between locations in a single cycle. By contrast in thecase of 16 bit data values, two 8 bit values have to be shifted pershift register shift operation (the HI half sheet and the LO halfsheet). In an embodiment, in the case of 32 bits, the same principlesapply except that four sheets are created to represent the entire imagedata rather than two sheets. Likewise, as many as four cycles may needto be consumed per shift sequence. Note that the discussion of 8 bitregister widths is only exemplary. Generally any bit width is possible(e.g., 16 bit wide registers within the register file with 32 bit widecircuitry internal to the execution lane).

FIG. 10 pertains to a compiler operation which unrolls random memoryaccesses so there are no competing memory accesses within the actualhardware during operation. Here, the procedure of FIG. 10 is directed tothe structuring of object code in view of the data being operated on byhigher level virtual code and the physical limitations of the underlyingmachine. As discussed previously, each execution lane in the executionlane array has an associated register file (e.g., four registers perexecution lane). Like most execution lanes, the execution lane readsand/or writes data from/to the registers consistent with the object codeinstructions. The compiler, like most compilers, is conscious of whatdata resides in what register and recognizes the physical limitations ofthe available register space.

As such, from time to time an execution lane may need a data item thatis not in register space but is instead located in a random accessmemory that is associated with an execution lane's row and/or column inthe execution lane array. Likewise, from time to time an execution lanemay need to write a data item but there is no register space into whichthe data can be written (because all data currently within registerspace still has dependencies). In these circumstances the compiler willinsert memory load or memory store instructions into the object code (asopposed to register load or register store instructions) to fetch/writedata from/to random access memory rather than register space.

FIG. 10 depicts an embodiment of the hardware architecture showing aseparate random access memory 1007_1 through 1007_R along each row ofthe array. From this architecture, execution lane s along a same row ofthe execution lane array are given access to a same random accessmemory. As drawn, each execution lane includes a memory unit foraccessing its respective random access memory. Accordingly, when twodifferent execution lane s on different rows execute a memory loadinstruction during a same cycle the instructions are not competingbecause they are directed to different random access memories.

By contrast if execution lane s on a same row are to perform a memoryaccess on a same cycle the memory access will compete. Given that theexecution lane array is intended to operate in a SIMD like fashion, theprogram code will naturally cause execution lane s in the array (whichincludes both rows and columns) to issue memory access requests on asame cycle. Thus, competing memory access from execution lane s on asame row is a foreseeable hazard. FIG. 10 shows a pair of threads 1001for execution on two different execution lane s on a same row. Given theSIMD-like nature of the machine both execution lane s execute sameopcodes in same cycles including a pair of memory load instructions inthe first two depicted cycles. Examining the addresses of the memoryload instructions, note that all the addresses are different. Thus, thefirst memory load instruction of both threads truly compete with oneanother and the second memory load instruction of both threads trulycompete with one another.

As such, when the compiler imposes a memory load instruction into theobject code it also recognizes that memory load instructions will imposeconflicts for execution lane s that reside on a same row. In response,the compiler will impose sequential memory load instructions into thecode to effectively unroll the competing memory load instruction along asame row so that each execution lane is provided with its own reservedcycle for accessing the memory. In the example of FIG. 10, note that thefinal object code 1002 includes a sequence of four sequential memoryload instructions across four cycles to ensure that the memory access ofone execution lane does not interfere with the memory access of anotherexecution lane along the same row.

Note that the approach of FIG. 10 is particularly applicable to thelook-up table portion of the memory model discussed above in Section1.0. Here, recall that different execution lane s may use differentindexes in a same look up table to access different entries of a samelook up table in a same cycle. In an embodiment, the compiler willinstantiate a different copy of the same look up table into each randomaccess memory 1007_1 through 1007_R. Lookups may therefore be made intothe local table copy during a same cycle by execution lane s ondifferent rows. Such look-ups do not compete and the index of eachlook-up may be different. By contrast, look-ups performed by executionlane s along a same row will access the same look-up table in the samememory and will need be unrolled and performed sequentially. With theunrolling into sequential access the index values are permitted to bedifferent. In an embodiment the VLIW instruction format of the objectcode includes, along with an opcode for a mathematical operation, anopcode for a memory operation that further includes the identity of theexecution lane along a row that is actually supposed to execute theinstruction (the other execution lane s along the row treat it as ano-op).

In various embodiments the compiler treats atomic update instructionssimilarly to look-up tables. That is, memory space is reserved (e.g.,per row) in random access memories 1007_1 through 1007_R for atomicinstruction resultants. Non competing updates (e.g., from a samepositioned execution lane along different rows) are permitted to executeduring a same cycle whereas competing updates (e.g., by execution lane salong a same row) are unrolled into separate instructions. Atomic updateinstructions are often implemented by the compiler as read-modify-writeinstructions where a read is made of recent resultant data residing inan execution lane's register space, such data is operated onmathematically and then written into the specially reserved atomicupdates table.

e. Implementation Embodiments

It is pertinent to point out that the various image processorarchitecture features described above are not necessarily limited toimage processing in the traditional sense and therefore may be appliedto other applications that may (or may not) cause the image processor tobe re-characterized. For example, if any of the various image processorarchitecture features described above were to be used in the creationand/or generation and/or rendering of animation as opposed to theprocessing of actual camera images, the image processor may becharacterized as a graphics processing unit. Additionally, the imageprocessor architectural features described above may be applied to othertechnical applications such as video processing, vision processing,image recognition and/or machine learning. Applied in this manner, theimage processor may be integrated with (e.g., as a co-processor to) amore general purpose processor (e.g., that is or is part of a CPU ofcomputing system), or, may be a stand alone processor within a computingsystem.

The hardware design embodiments discussed above may be embodied within asemiconductor chip and/or as a description of a circuit design foreventual targeting toward a semiconductor manufacturing process. In thecase of the later, such circuit descriptions may take of the form ofhigher/behavioral level circuit descriptions (e.g., a VHDL description)or lower level circuit description (e.g., a register transfer level(RTL) description, transistor level description or mask description) orvarious combinations thereof. Circuit descriptions are typicallyembodied on a computer readable storage medium (such as a CD-ROM orother type of storage technology).

From the preceding sections is pertinent to recognize that an imageprocessor as described above may be embodied in hardware on a computersystem (e.g., as part of a handheld device's System on Chip (SOC) thatprocesses data from the handheld device's camera). In cases where theimage processor is embodied as a hardware circuit, note that the imagedata that is processed by the image processor may be received directlyfrom a camera. Here, the image processor may be part of a discretecamera, or, part of a computing system having an integrated camera. Inthe case of the later the image data may be received directly from thecamera or from the computing system's system memory (e.g., the camerasends its image data to system memory rather than the image processor).Note also that many of the features described in the preceding sectionsmay be applicable to a graphics processor unit (which rendersanimation).

FIG. 11 provides an exemplary depiction of a computing system. Many ofthe components of the computing system described below are applicable toa computing system having an integrated camera and associated imageprocessor (e.g., a handheld device such as a smartphone or tabletcomputer). Those of ordinary skill will be able to easily delineatebetween the two.

As observed in FIG. 11, the basic computing system may include a centralprocessing unit 1101 (which may include, e.g., a plurality of generalpurpose processing cores 1115_1 through 1115_N and a main memorycontroller 1117 disposed on a multi-core processor or applicationsprocessor), system memory 1102, a display 1103 (e.g., touchscreen,flat-panel), a local wired point-to-point link (e.g., USB) interface1104, various network I/O functions 1105 (such as an Ethernet interfaceand/or cellular modem subsystem), a wireless local area network (e.g.,WiFi) interface 1106, a wireless point-to-point link (e.g., Bluetooth)interface 1107 and a Global Positioning System interface 1108, varioussensors 1109_1 through 1109_N, one or more cameras 1110, a battery 1111,a power management control unit 1112, a speaker and microphone 1113 andan audio coder/decoder 1114.

An applications processor or multi-core processor 1150 may include oneor more general purpose processing cores 1115 within its CPU 1101, oneor more graphical processing units 1116, a memory management function1117 (e.g., a memory controller), an I/O control function 1118 and animage processing unit 1119. The general purpose processing cores 1115typically execute the operating system and application software of thecomputing system. The graphics processing units 1116 typically executegraphics intensive functions to, e.g., generate graphics informationthat is presented on the display 1103. The memory control function 1117interfaces with the system memory 1102 to write/read data to/from systemmemory 1102. The power management control unit 1112 generally controlsthe power consumption of the system 1100.

The image processing unit 1119 may be implemented according to any ofthe image processing unit embodiments described at length above in thepreceding sections. Alternatively or in combination, the IPU 1119 may becoupled to either or both of the GPU 1116 and CPU 1101 as a co-processorthereof. Additionally, in various embodiments, the GPU 1116 may beimplemented with any of the image processor features described at lengthabove.

Each of the touchscreen display 1103, the communication interfaces1104-1107, the GPS interface 1108, the sensors 1109, the camera 1110,and the speaker/microphone codec 1113, 1114 all can be viewed as variousforms of I/O (input and/or output) relative to the overall computingsystem including, where appropriate, an integrated peripheral device aswell (e.g., the one or more cameras 1110). Depending on implementation,various ones of these I/O components may be integrated on theapplications processor/multi-core processor 1150 or may be located offthe die or outside the package of the applications processor/multi-coreprocessor 1150.

In an embodiment one or more cameras 1110 includes a depth cameracapable of measuring depth between the camera and an object in its fieldof view. Application software, operating system software, device driversoftware and/or firmware executing on a general purpose CPU core (orother functional block having an instruction execution pipeline toexecute program code) of an applications processor or other processormay perform any of the functions described above.

Embodiments of the invention may include various processes as set forthabove. The processes may be embodied in machine-executable instructions.The instructions can be used to cause a general-purpose orspecial-purpose processor to perform certain processes. Alternatively,these processes may be performed by specific hardware components thatcontain hardwired logic for performing the processes, or by anycombination of programmed computer components and custom hardwarecomponents.

Elements of the present invention may also be provided as amachine-readable medium for storing the machine-executable instructions.The machine-readable medium may include, but is not limited to, floppydiskettes, optical disks, CD-ROMs, and magneto-optical disks, FLASHmemory, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards,propagation media or other type of media/machine-readable mediumsuitable for storing electronic instructions. For example, the presentinvention may be downloaded as a computer program which may betransferred from a remote computer (e.g., a server) to a requestingcomputer (e.g., a client) by way of data signals embodied in a carrierwave or other propagation medium via a communication link (e.g., a modemor network connection).

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

The invention claimed is:
 1. A computing device comprising: an array ofexecution lanes; a scalar lane; a two-dimensional shift-register array;and a sheet generator configured to load sheets of data into thetwo-dimensional shift register array, wherein the computing device isconfigured to perform operations comprising: receiving, by the scalarlane, an instruction specifying an operation to be performed using anoperand having a first bit width, wherein the first bit width is widerthan a second bit width of shift registers in the shift-register array;issuing one or more instructions to the sheet generator that cause thesheet generator to load a high sheet and a low sheet into theshift-register array of the computing device; and providing, by thescalar lane to each of the execution lanes in the execution lane array,one or more instructions to perform the operation using the operandhaving the first bit width using data from the high sheet and the lowsheet loaded into the shift-register array.
 2. The computing device ofclaim 1, wherein the execution lanes are configured to use data from thehigh sheet and the low sheet loaded into the shift-register array byperforming operations comprising: performing a first read from the highsheet stored in the shift-register array to obtain a first portion ofthe operand; and performing a second read from the low sheet stored inthe shift-register array to obtain a second portion of the operand. 3.The computing device of claim 2, wherein the execution lanes areconfigured to store respective portions of the result of executing theone or more instructions into the high sheet and the low sheet of theshift-register array by performing operations comprising: performing afirst write of a first portion of the result to the high sheet stored inthe shift-register array; and performing a second write of a secondportion of the result to the low sheet stored in the shift-registerarray.
 4. The computing device of claim 3, wherein the scalar lane isconfigured to receive a shift instruction that specifies shifting datain the high sheet and the low sheet in the shift-register array andwherein the scalar lane is configured to issue multiple shiftinstructions to each execution lane to separately shift the high sheetand the low sheet in a same direction.
 5. The computing device of claim1, wherein the first bit width of the operand is twice the second bitwidth of the shift registers.
 6. The computing device of claim 1,wherein the first bit width of the operand is four times the second bitwidth of the shift registers.
 7. The computing device of claim 6,wherein the execution lanes are configured to use data from twoadditional sheets of data loaded into the shift-register array byperforming operations comprising: performing a first read from a firstadditional sheet stored in the shift-register array to obtain a firstportion of the operand; and performing a second read from a secondadditional sheet stored in the shift-register array to obtain a secondportion of the operand.
 8. A method performed by computing device havingan array of execution lanes, a scalar lane, a two-dimensionalshift-register array, and a sheet generator configured to load sheets ofdata into the two-dimensional shift-register array, the methodcomprising: receiving, by the scalar lane, an instruction specifying anoperation to be performed using an operand having a first bit width,wherein the first bit width is wider than a second bit width of shiftregisters in the shift-register array; issuing one or more instructionsto the sheet generator that cause the sheet generator to load a highsheet and a low sheet into the shift-register array of the computingdevice; and providing, by the scalar lane to each of the execution lanesin the execution lane array, one or more instructions to perform theoperation using the operand having the first bit width using data fromthe high sheet and the low sheet loaded into the shift-register array.9. The method of claim 8, further comprising using, by the executionlanes, data from the high sheet and the low sheet loaded into theshift-register array comprising: performing a first read from the highsheet stored in the shift-register array to obtain a first portion ofthe operand; and performing a second read from the low sheet stored inthe shift-register array to obtain a second portion of the operand. 10.The method of claim 9, further comprising storing, by the executionlanes, respective portions of the result of executing the one or moreinstructions into the high sheet and the low sheet of the shift-registerarray comprising: performing a first write of a first portion of theresult to the high sheet stored in the shift-register array; andperforming a second write of a second portion of the result to the lowsheet stored in the shift-register array.
 11. The method of claim 10,further comprising: receiving, by the scalar lane, a shift instructionthat specifies shifting data in the high sheet and the low sheet in theshift-register array; and issuing, by the scalar lane, multiple shiftinstructions to each execution lane to separately shift the high sheetand the low sheet in a same direction.
 12. The method of claim 8,wherein the first bit width of the operand is twice the second bit widthof the shift registers.
 13. The method of claim 8, wherein the first bitwidth of the operand is four times the second bit width of the shiftregisters.
 14. The method of claim 13, further comprising using, by theexecution lanes, data from two additional sheets of data loaded into theshift-register array comprising: performing a first read from a firstadditional sheet stored in the shift-register array to obtain a firstportion of the operand; and performing a second read from a secondadditional sheet stored in the shift-register array to obtain a secondportion of the operand.
 15. One or more non-transitory computer storagemedia encoded with instructions to be executed by a computing devicecomprising an array of execution lanes, a scalar lane, a two-dimensionalshift-register array, and a sheet generator configured to load sheets ofdata into the two-dimensional shift register array, wherein theinstructions comprise an instruction specifying an operation to beperformed using an operand having a first bit width, wherein the firstbit width is wider than a second bit width of shift registers in theshift-register array, and wherein executing the instruction causes thecomputing device to perform operations comprising: issuing one or moreinstructions to the sheet generator that cause the sheet generator toload a high sheet and a low sheet into the shift-register array of thecomputing device; and providing, by the scalar lane to each of theexecution lanes in the execution lane array, one or more instructions toperform the operation using the operand having the first bit width usingdata from the high sheet and the low sheet loaded into theshift-register array.
 16. The one or more non-transitory computerstorage media of claim 15, wherein the operations further compriseusing, by the execution lanes, data from the high sheet and the lowsheet loaded into the shift-register array comprising: performing afirst read from the high sheet stored in the shift-register array toobtain a first portion of the operand; and performing a second read fromthe low sheet stored in the shift-register array to obtain a secondportion of the operand.
 17. The one or more non-transitory computerstorage media of claim 16, wherein the operations further comprisestoring, by the execution lanes, respective portions of the result ofexecuting the one or more instructions into the high sheet and the lowsheet of the shift-register array comprising: performing a first writeof a first portion of the result to the high sheet stored in theshift-register array; and performing a second write of a second portionof the result to the low sheet stored in the shift-register array. 18.The one or more non-transitory computer storage media of claim 17,wherein the operations further comprise: receiving, by the scalar lane,a shift instruction that specifies shifting data in the high sheet andthe low sheet in the shift-register array; and issuing, by the scalarlane, multiple shift instructions to each execution lane to separatelyshift the high sheet and the low sheet in a same direction.
 19. The oneor more non-transitory computer storage media of claim 15, wherein thefirst bit width of the operand is twice the second bit width of theshift registers.
 20. The one or more non-transitory computer storagemedia of claim 15, wherein the first bit width of the operand is fourtimes the second bit width of the shift registers.